On the most recent episode of The Talk Show, John Gruber mentioned his desire for a trackpad to feature on the next version of Apple's Smart Keyboard. A while back I had an idea for how such a thing might work, without requiring the addition of a laptop-style trackpad area. My idea is analogous to 'trackpad mode' on the iOS software keyboard (accessed via two fingers on the iPad, or via 3D Touch on the iPhone).
The keys on the Smart Keyboard are very low profile, so it's easy for one's fingers to glide over them. With this in mind, why not make the entire top surface of the keyboard touch sensitive, then use it in the same way as the software keyboard? All that's needed is a way to toggle trackpad mode, and I think this is a perfect opportunity to ditch the 'caps lock' key, and replace it with a 'trackpad mode' key, which can be held down while using one's other finger to move the cursor.
There are a few reasons why I think this approach would be better than a discrete trackpad. First, it requires no extra space, nor any major changes to the current design. Second, as mentioned above, it maintains gesture parity with the current trackpad mode on iOS. Third, it removes the expectation of a system-wide, mouse-style pointer, which I think a laptop-style trackpad would create. I think this is a significant consideration; a more precise pointing device would be really useful on iOS for more than just text entry, but I don't expect this to come in the form of a mouse pointer. Thus, I think avoiding the suggestion of one altogether would lead to less confusion. With my proposed method, pro users who need this functionality won't take long to become aware of it, and users who don't need it won't have what they may perceive as a half-broken laptop trackpad present at all times.
Click the title link to see a video mocking up what this might look like.